Frequency changer



Patented Sept. 4, 1945 FREQUENCY CHANGER Henry Martin Huge, Lorain, Ohio, assignor of .one-half to E. M. Heavens and one-half to Closman P. Stocker Application October 9, 1943, Serial No. 505,611

13 Claims.

This invention relates to frequency changers and in particular to a frequency-changing transformer capable of generating subharmonics of the input frequency. The subject matter of this application is an extension of the invention shown and described in my copending application Serial No. 485,834, filed May 6, 1943, now Patent No. 2,364,532 dated Dec. 5, 1944.

It is an object of this invention to generate subharmonics of the input frequency in a static frequency changer.

Another object of this invention is to produce a frequency-changing transformer for the generationof su-bharmonics.

Another object of this invention is to produce a subharmonic generator of high efliclency and stability.

Still another object of this invention is to antomatically stant subharmonic oscillations by means of a relay.

Other objects and a better understanding of my invention may be had by referring to the following specification and claims together with the accompanying drawings, in which:

Figure 1 shows diagrammatically a subharmonic generator made according to my invention,

with a three-legged saturable magnetic core;

Figure 2 is a modification of the arrangement of Figure 1 with windings on all three of the core members;

Figure 3 is a modification of the arrangement of Figure 2, with paralleled windings, an overload protection capacitor and a saturable inductance for introducing harmonics in the subharmonic output voltage;

Figure 4 is another modification of the arrangement of Figure 2, in which the input is applied to two or" the core members, and

figure 5 shows a further modification of my invention. using a common magnetic core. With this construction the unit may be made in two separate and distinct pieces each piece including the windings shown on one member of Fig. 5.

With more particular reference to Figure 1, there is shown a magnetic core structure having three members, it, it, and I'l. Winding it on member ll is energized from source it].

When the power from source it is first applied, the normallyciosed relay contacts 20 supply voltage to capacitor I4. The current through capacitor It and relay winding it operates the relay and opens contacts 20. The charge on capacitor it when the relay contacts open flows off through winding ii on core member I5, ma netizing the core and starting the subharmonic oscillation through winding II and capacitor I4. The subharmonic current through capacitor I4 and relay winding I9 holds open the rela contacts 20 asv long as the oscillation continue, but, should they stop, the relay releases, closing contacts 20 and restarting the oscillations.

In operation, the flux through core member I! is mostly of the frequency of source I0, because winding I3 is connected directly to the source. Because capacitor I 4 has a low impedance at the frequency of source I0, it tends to keep flux of that frequency out of core member I5 and most of the flux through I1 is driven to member I6 for its return path. Thus core member I6 acts as a saturable leakage reactance between the primary winding I3 and the secondary winding ll, Since source I0 normally has a low impedance to the subharmonic frequency, most of the subharmonic flux through member I5 is also driven to member I6 for its return path. Thus the subharmonic flux flows around through core members I5 and I6 and the energizing flux flows around through members I6 and IT. The superposition of fluxes in member I6 saturates this core member and thereby sustains and stabilizes the subharmonic oscillations. It may be desirable to increase the starting voltage upon capacitor I4. This may be done by connecting the starting contact on relay I9 to a tap (not shown) on winding II. This will provide a step-up in voltage supplied to condenser I4 during the starting condition.

The load in Figure l is shown connected di rectly across winding II, and may be supplied with voltage which is predominantly subharmonic with a relatively small component of the frequency of source I0. The output frequency most easily produced is one-third the input frequency, but other subharmonics can also be produced when the elements are suitably proportioned.

Figure 2 shows a modification of the arrangement of Figure 1, with winding I2 added on core member I6 and connected in series with windings II and I3. If windings II, I2, and I3 all have substantially the same number of turns, the energizing arrangement of Figure 2 may become substantially equivalent to that of Figure 1. The truth of this statement becomes evident when it is observed that when windings IE and are polarized in the same direction, they can produce in core member I? substantially the same eiiect as that produced by Winding I3, so that the change from Figure l to Figure 2 in this case con sists of taking half of winding I3 in Figure 1 and replacing Figure 2. In addition, output winding II on core member I! to supply the subharmonic power to the load. Furthermore, relay contacts III in Figure 2 are connected across winding II, but the efiect is as in Figure 1, i. e. the closed contacts apply voltage from source I. to capacitor ll.

It is not necessary to make windings H, II, and IS in Figure 2 all equal; in fact, I have found that improved operation can be obtained by making winding II with fewer turns than either winding I2 or winding l3, particularly when core member I5 has a larger cross-sectional area than either member Ii or II. With this arrangement, part of the subharmonic flux flows through core member I I. Since core member I! is normally saturated, this arrangement increases the subharmonic flux density in core member l5. thereby making better use of this core member. Furthermore, since the conversion of power from the input frequency to the subharmonic frequency can occur only in a core member in which the fluxes of the two frequencies are superimposed, the addition of the subharmonic flux in core member ll produces an added advantage. I have also found that as the number of turns on winding i I is reduced, the turns on windings l2 and I3 may also be reduced somewhat without increasing the input current to the transformer. With the subharmonic flux flowing through both core members l6 and I? and with primary windings on all three legs of the core, it is no longer clearly evident that there is a saturable leakage reactance between the primary windings and the secondary (or capacitor) winding, although in effect this is still true.

With the circuit shown in Figure 2, capacitor i4 may have applied to it a relatively low voltage and the design may not be economical because of the large capacity required. This difllculty is overcome by putting more turns on winding H and providing the winding with taps for the primary circuit as is shown in Figure 3. This fi are also shows several other modifications, one being a double winding arrangement to facilitate operation on either of two input voltages. The connection shown is for the lower input voltage, with windings 2i and 25 in series, windings 22 and 23 in series and the two series combinations connected in parallel and connected to terminal 2? on winding ii. For operation on twice this voltage, windings 2!, 24, 22, and 23 are connected in series and connected to terminal 26 on winding ii. The operation is substantially the same on either the high or the low input voltage.

The relay contacts 20 in Figure 3 are connected across windin H on core member l6. When the power from source ID is first applied, the shorted winding keeps most of the flux out of core member 58, driving it through the center member l5, where it induces voltage across capacitor ll. The current through capacitor l4 and relay winding 59 opens the relay contacts 20. The charge which is on capacitor H when the relay contacts open then flows on through winding ll, magnetizing the core and causing subharmonic oscillations to start in the circuit of winding H. The subharmonic current through relay winding 29 keeps the contacts 20 open as long as the oscillations continue, if they stop the relay releases and restarts the oscillations.

Figure 3 shows an arrangement for introducing high order harmonics into the output voltage. These harmonics are frequently required when it by windings H and I! in seriesin Figure 2 has an insulated the converter is used to supply telephone ringing current, in which case the audible components of the output voltage may be fed back to the calling subscriber's receiver to let him hear when the bell of the called subscriber is being rung. The audible components of the pure ringing voltage supplied by the converters of Figures 1 and 2 are usually too weak for this purpose so the saturable inductance havin windings 28 and 20 is added in the circuit of Figure 3, together with capacitor 30. Saturable inductance winding 18 in series with capacitor I4 is energized with subharmonic current which, because of the saturation of the magnetic core, generates high order harmonics in the voltage across windings 2! and 29. Capacitor ill in parallel with winding 28 accentuates the desired harmonics and winding 29 is connected in series with output winding II. This combination is more fully described in my patent application of May 8, 1942, Serial No. 442,224, now pending.

Capacitor 25 in series with the output winding I8 acts as an overload protective device. When the load current becomes excessive, capacitor 25 drops the load voltage and insures that the subharmonic oscillations will not be stopped by overloads. This protection prevents excessive use of the relay, since the relay releases each time the oscillations stop and thereby restarts them.

Figure 4 shows another modification of the circuit of Figure 2, in which the primary windings are placed on only the two outer core members l5 and i1. This arrangement can be made to produce substantially the same results as produced by the arrangement of Figure 2. In the circuit of Figure 4, I prefer to make winding H with fewer turns than winding I3, thus producing an unsymmetrical magnetization of the core as is produced in Figure 2 by the action of winding H in series with windings i2 and I3.

The windings l2 and IS in Figure 4 may be made substantially equal but in this case I prefer to make one of the core members 18 and I! smaller in cross sectional area or otherwise magnetically dissimilar to the other, so that an unbalanced condition exists, producing an externally applied magnetornotive force of the source frequency across core member [5. Actually, very little flux of the source frequency flows through 15, since it is stopped by the action of the lowimpedance capacitor l4, which readily passes current of the source frequency to produce a counter-magnetomotive force of the source frequency. I have found that the unbalanced condition is essential to stability 01 operation, and that when insufficient unbalance is present the frequency of the output voltage may change under variations of load current. The unbalanced condition is characterized by the current of the source frequency which it induces in capacitor it, even though this current produces little voltage across the capacitor. In all the arrangements shown, there is relatively more subharmonic flux in member l6 than in H. In particular, in the arrangement of Figure 1 there is practically no subharmonic flux in member I1.

The operation of the transformer of Figure 4 is similar to that described in connection with Fisure 2. The flux through core member 15 is predominantly subharmonic flux, and it circulates through both of the outer members I! and I1 on its return path but does not divide equally between them. The ratio between the amounts of subharmonic flux through core members It and I1 depends on the relative number of turns on windings I2 and It in Figure 4.' The flux of the frequency of source III circulates chiefly through core members I6 and I1, inducing in windings I2 and I3 voltages which add together, their sum being substantially equal to the voltage of source III. In this description source It is considered as being a generator of low internal impedance so that the voltage appearing across it is influenced only slightly by the current through windings I2 and I3, and will include very little subharrnonic voltage. In this case the subharmonic flux through core member I1 produces a subharmonic voltage which substantially cancels that induced in winding I2 by the subharmonic flux in member I8.

As with the arrangements of Figures 1, 2, and 3, the circuit of Figure 4 is best adapted to supply the load with power at a frequency which is one-third the frequency of source III, but other frequencies can be supplied with the circuit elements suitably proportioned.

Figure 5 shows another modification of my frequency changer in which all the windings are placed on two of the three core members. Winding II of the previous figures is replaced by windings 3I and 32 and output winding I8 by windings 33 and 34. With the arrangement of Figure 5 the operation of the frequency changer of Figure 4 may be substantially duplicated, but it is also possible to modify some of the operating conditions. For example, in the arrangements of Figures 1 to 4 there is relatively little flux of the input frequency through member I5, but in Figure 5 if windings 3| and 32 are dissimilar, there may be appreciable flux of the input frequency through member I 5. This does not imply that there is any fundamental difference between the operation of the arrangement of Figure 5 and that obtainable with the arrangements of Figures 1 to 4, since the same essential features are present in all the arrangements. These features are, the primary winding or windings for energizing the saturable core from the alternatin current source, the secondary winding or windings connected to the capacitor for sustaining the subharmonic oscillations and the unbalanced core or winding arrangement which effectively provides a saturable leakage reactance between primary and secondary,

To confirm the presence of the saturable leakage reactance between primary and secondary in any of the arrangements pictured, it is well to consider the nature of the secondary current when the secondary is short-circuited. arrangement of Figure 1 it is apparent that the short-circuit. current in winding II will be just that which is required to magnetize core member I6, therefore when the primary voltage is relatively low, very little secondary current will flow, as it will require little force to magnetize I6 at the low flux density but if the primary voltage is increased until the member I6 begins to saturate, the secondary current will increase to the value necessary to magnetize I6 at the high flux density.

In Figure 2 it is apparent that if secondary winding II is shorted by an ammeter, the meter will carry the same exciting current as windings I2 and I3 and the current will therefore exhibit the same rapid increase at high voltage as experienced with the arrangement of Figure 1, and it can be said that there is effectively a saturable leakage reactance between the primary and the In the secondary in Figure 2. In this respect Figure 3 is similar to Figure 2.

The arrangement of Figure 4 is somewhat similar to that of Figure 1 except that core member I8 already has part of its magnetizing force supplied by winding I 2 so that the short-circuit current of winding II need only supply the remainder, but the saturation effect will (be in evidence as before. If the structure is perfectly balanced, however, there will be no short-circuit current in winding II, therefore it will no longer be correct to state that a saturable leakage reactance exists between primary and secondary, but, as previously stated, my invention does not contemplate the use of a perfectly balanced structure.

The characteristics of the arrangement of Figure 5 parallel those of Figure 4, even [when pri-' mary flux is caused to flow in all three core members.

It is to be understood that the drawings are diagrammatic in nature and do not necessarily represent the proportions of the magnetic core or windings thereon.

Although I have described my invention with a certain degree of particularity, it is to be understood that the present disclosure has been made only by way of example, and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

I claim as my invention:

1. A subharmonic generator comprising in combination a magnetic core having a plurality of core members, a first winding on one of said members adapted to be energized by a source of alternating current, a second winding on another of said members, a capacitor connected across a id second winding, and a relay having normally closed contacts connecting said capacitor to said first winding to supply energy from the source of alternating current to the capacitor when the relay contacts are closed, said relay being adapted to be energized with subharmonic current.

2. A frequency reducer comprising in combination a magnetic core having a plurality of core members, a first winding on one of said core members adapted to be energized by a source of alternating current, a second winding on another of said core memers, a, capacitor connected across said second winding, a relay adapted to be energized with current of the reduced frequency, said second winding being adapted to be energized at the frequency of said source until said relay opcrates, and then energized at the reduced frequency.

3. A subharmonic generator adapted to be energized by a source of alternating current and to supply a load with power at a subharmonic frequency, comprising in combination a magnetic core having first, second, and third core members, windings on said first and second core members adapted to be energized by the source of alternating current, a winding on said third core member, a capacitor connected across said winding on the third core member, and a relay adapted to supply an intitial charge to said capacitor to start subharmonic oscillations through the capacitor.

4. A subharmonic generator comprising in combination magnetic core means having at least three core members, primary winding means on the core means adapted to be energized by a source of alternating current, secondary winding means on the core means, capacitive means connected across the secondary winding means, and starting means comprising a relay adapted to produce a starting transient in the secondary winding means to initiate subharmonic oscillations therein, said primary and secondary winding means being disposed on at least two of the core members and having effectively a saturable leakage reactance between them.

5. A subharmonic generator comprising in combination, magnetic core means having at least three core members, primary winding means on the core means adapted to be energized by a source of alternating current, secondary wind ing means on the core means, capacitive means energized by the secondary winding means, starting means adapted to produce a starting transient to initiate subharmonic oscillations through the capacitive means, and output winding means inductively related to the secondary winding means, said winding means being disposed on at least two of the core members with an effective saturable leakage reactance between the primary and secondary Winding means. I

6. A frequency reducer comprising in combination a magnetic core having first, second, and third core members, the first and second core members having substantially the same magnetic characteristics, first and second substantially equal windings respectively on said first and second core members adapted to be energized from a source of alternating current and to produce opposing fiuxes in the third core member, a third winding on the third core member, a capacitor adapted to be energized from said third winding, at least a portion of the third winding being adapted to be energized from the source in series with the first winding, and starting means adapted to init ate oscillations of the reduced frequency in the third winding means.

'7. A frequency reducer comprising in combination a magnetic core having first, second, and third core members, the first and second core members having substantially the same magnetic characteristics, first and second substantially equal windings respectively on said first and second core members adapted to'be energized from a source of alternating current and to produce opposing fluxes in the third core member, a third winding on the third core member, a capacitor adapted to be energized from said third winding, at least a portion of the third winding being adapted to be energized from the source in series with the first winding, starting means adapted to initiate oscillations of the reduced frequency in the third winding means and an output circuit for supplying the reduced frequency to a load.

8. A frequency reducing arrangement comprising in combination a magnetic core having first, second, and third core members with first, second, and th rd windings respectively thereon, the first, second. and third windings being connected in series and adapted to be energized by an al ternating current source, a capacitor adapted to be energized from the third winding, a starting relay adapted to produce an initial charge on the capacitor to initiate oscillations of the reduced frequency through it, and an output circuit for supplying the reduced frequency to a load.

9. A subharmonic generator comprising in combination a magnetic core having first, second. and third core members, first and second unequal windings on the first and second core members respectively, said first and second windings being connected in series and adapted to be energized by an alternating current source and to produce opposing fluxes in the third core member, a third winding on the third core member, a capacitor connected across the third winding for supporting subharmonic oscillations therein, an output winding on the third core member and a starting relay having normally closed contacts shunting at least a portion of the first winding.

10. A subharmonic generator comprising in combination a magnetic core having first, second, and third core members, the first and second core members being magnetically dissimilar, first and second windings on the first and second core members respectively, said first and second windings being connected in series and adapted to be energized by a source of alternating current and to produce opposing fiuxes in the third core member, a third winding on the third core member, a capacitor connected across the third winding for supporting subharmonic oscillations therein, an output winding on the third core member, and a starting relay having normally closed contacts shunting at least a portion of the first winding.

11. A subharmonic generator comprising in combination a saturable magnetic core having first, second, and third core members, a primary circuit comprising'windings on the first and second core members connected in series and adapted to be energized by a source of alternating current and to produce opposing fluxes in the third core member, a secondary circuit comprising windings on the first and second core members connected in series opposition with respect to said primary windings, a capacitor connected across the secondary circuit, a relay adapted to produce a starting transient to initiate subharmonic oscillations in the secondary circuit, and an output circuit inductively related to said secondary c rcuit.

12. A subharmonic generator comprising in combination a saturable magnetic core having first, second, and third core members, a primary circuit comprising windings on the first and second core members connected in series and adapted to be energized by a source of alternating current and to produce opposing fluxes in the third core member, a secondary circuit comprising windings on the first and second core members connected in unbalanced series opposition with respect to said primary windings, a capacitor connected across the secondary circuit, a relay adapted to produce a starting transient to initiate subharmonic oscillations in the secondary circuit, and an output circuit inductively related to said secondary circuit.

13. A subharmonic generator comprising in combination, first and second saturable magnetic flux paths, a primary circuit comprising windings on the first and secondfiux paths, connected in series and adapted to be energized by a source of alternating current, a secondary circuit comprising windings on the first and second flux paths connected in unbalanced series opposition with respect to said primary windings, a capacitor connected across the secondary circuit, a relay adapted to produce a starting transient to initiate subharmonic oscillations in the secondary circuit, and an output circuit inductively related to said secondary circuit.

HENRY MARTIN HUGE. 

